Chemistry of materials under extreme high pressure-high-temperature conditions

Most of our knowledge of chemistry is derived from experiments carried at the Earth's surface, at pressures near one atmosphere. However, most elements and compounds in the universe exist under conditions of extremely high pressures, often combined with high temperatures, deep within the planets and stars. Under these conditions, new high-density crystal forms occur, species usually known only as molecules become dense covalent or ionic solids, and insulators and semiconductors become metals and even superconductors. Valency states and coordination numbers are changed, and it is expected that chemical bonding and reactivity is modified. Paul McMillan describes how the field of condensed matter chemistry under extreme high pressure conditions now represents a vast new area to be explored.     

Connecting the philosophy of chemistry,green chemistry,and moral philosophy

This paper aims to connect philosophy of chemistry, green chemistry, and moral philosophy. We first characterize chemistry by underlining how chemists: (1) co-define chemical bodies, operations, and transformations; (2) always refer to active and context-sensitive bodies to explain the reactions under study; and (3) develop strategies that require and intertwine with a molecular whole, its parts, and the surroundings at the same time within an explanation. We will then point out how green chemists are transforming their current activities in order to act upon the world without jeopardizing life. This part will allow us to highlight that green chemistry follows the three aforementioned characteristics while including the world as a partner, as well as biodegradability and sustainability concerns, into chemical practices. In the third part of this paper, we will show how moral philosophy can help green chemists: (1) identify the consequentialist assumptions that ground their reasoning; and (2) widen the scope of their ethical considerations by integrating the notion of care and that of vulnerability into their arguments. In the fourth part of the paper, we will emphasize how, in return, this investigation could help philosophers querying consequentialism as soon as the consequences of chemical activities over the world are taken into account. Furthermore, we will point out how the philosophy of chemistry provides philosophers with new arguments concerning the key debate about the ‘intrinsic value’ of life, ecosystems and the Earth, in environmental ethics. To conclude, we will highlight how mesology, that is to say the study of ‘milieux’, and the concept of ‘ecumeme’ proposed by the philosopher and geographer Augustin Berque, could become important both for green chemists and moral philosophers in order to investigate our relationships with the Earth.     

Autowave modes of polymerization and other reactions in solid frozen matrixes near of absolute zero and their role in mechanisms of fast chemical transformations of substance in universe

Almost two decades ago there were discovered new autowave selfpropagation phenomena in the cryo‐chemical reactions at investigating of chemical solid phase transformations near absolute zero of temperatures. Such an autowave regime is observed for different classes of chemical reactions (polymerisation, copolymerisation and also hydrocarbon halogenation, hydro‐halogenation etc). The chemical transformations studied at the such low temperatures 4–77 K proceeded with so great rates that they can be compared only with the fastest high‐temperature combustion reactions known in chemistry. It allows to advance a principally new autowave conception of the matter chemical activity in solid state. The essentially non‐Arrenius conception is based on the assumption that a mechanical energy accumulated in solid matrix can be transformated to the chemical forms.     

Dynamic imine chemistry

Formation of an imine--from an amine and an aldehyde--is a reversible reaction which operates under thermodynamic control such that the formation of kinetically competitive intermediates are, in the fullness of time, replaced by the thermodynamically most stable product(s). For this fundamental reason, the imine bond has emerged as an extraordinarily diverse and useful one in the hands of synthetic chemists. Imine bond formation is one of a handful of reactions which define a discipline known as dynamic covalent chemistry (DCC), which is now employed widely in the construction of exotic molecules and extended structures on account of the inherent 'proof-reading' and 'error-checking' associated with these reversible reactions. While both supramolecular chemistry and DCC operate under the regime of reversibility, DCC has the added advantage of constructing robust molecules on account of the formation of covalent bonds rather than fragile supermolecules resulting from noncovalent bonding interactions. On the other hand, these products tend to require more time to form--sometimes days or even months--but their formation can often be catalysed. In this manner, highly symmetrical molecules and extended structures can be prepared from relatively simple precursors. When DCC is utilised in conjunction with template-directed protocols--which rely on the use of noncovalent bonding interactions between molecular building blocks in order to preorganise them into certain relative geometries as a prelude to the formation of covalent bonds under equilibrium control--an additional level of control of structure and topology arises which offers a disarmingly simple way of constructing mechanically-interlocked molecules, such as rotaxanes, catenanes, Borromean rings, and Solomon knots. This tutorial review focuses on the use of dynamic imine bonds in the construction of compounds and products formed with and without the aid of additional templates. While synthesis under thermodynamic control is giving the field of chemical topology a new lease of life, it is also providing access to an endless array of new materials that are, in many circumstances, simply not accessible using more traditional synthetic methodologies where kinetic control rules the roost. One of the most endearing qualities of chemistry is its ability to reinvent itself in order to create its own object, as Berthelot first pointed out a century and a half ago.     

Conceptual density functional theory under pressure: Part I. XP-PCM method applied to atoms

High pressure chemistry offers the chemical community a range of possibilities to control chemical reactivity, develop new materials and fine-tune chemical properties. Despite the large changes that extreme pressure brings to the table, the field has mainly been restricted to the effects of volume changes and thermodynamics with less attention devoted to electronic effects at the molecular scale. This paper combines the conceptual DFT framework for analyzing chemical reactivity with the XP-PCM method for simulating pressures in the GPa range. Starting from the new derivatives of the energy with respect to external pressure, an electronic atomic volume and an atomic compressibility are found, comparable to their enthalpy analogues, respectively. The corresponding radii correlate well with major known sets of this quantity. The ionization potential and electron affinity are both found to decrease with pressure using two different methods. For the electronegativity and chemical hardness, a decreasing and increasing trend is obtained, respectively, and an electronic volume-based argument is proposed to rationalize the observed periodic trends. The cube of the softness is found to correlate well with the polarizability, both decreasing under pressure, while the interpretation of the electrophilicity becomes ambiguous at extreme pressures. Regarding the electron density, the radial distribution function shows a clear concentration of the electron density towards the inner region of the atom and periodic trends can be found in the density using the Carbó quantum similarity index and the Kullback–Leibler information deficiency. Overall, the extension of the CDFT framework with pressure yields clear periodic patterns.

Conceptual DFT has provided a framework in which to study chemical reactivity. Since high pressure is more and more a tool to control reactions and fine-tune chemical properties, this variable is introduced into the CDFT framework.     

有机二硫化物润滑添加剂抗磨极压性能的密度泛函理论研究

用量子化学的密度泛函理论计算了12种有机二硫化物和铁原子簇的分子轨道指数及其与铁原子簇的化学吸附作用能, 探讨了这种作用能与抗磨性能的关系; 运用轨道能量近似原则讨论了有机二硫化物与铁原子的作用方式; 以前线电子密度、超离域性指数和原子净电荷作为判据分析了12种有机二硫化物与铁原子间键合的强弱、反应性的大小等表征有机二硫化物与金属作用强弱的参数。结果表明: 有机二硫化物与铁接触时, 在较缓和条件下, SS键优先断裂与金属发生化学吸附形成配位键, 起到抗磨作用; 在高负荷下, 与金属发生常规条件下不能发生的化学反应, 即CS键断裂生成无机膜, 起到极压作用; 且随着碳链的增长, 有机二硫化物的抗磨性能愈来愈好, 但极压性能愈来愈差; 运用量子化学计算得到的预测结果与摩擦学试验结果具有良好的一致性, 可为同类极压添加剂化合物的分子设计提供较为可靠的参考依据和理论方法。     

我和氢的故事

氢是宇宙中最丰富的元素,在通常条件和高温、低温、高压等极端条件下都表现出重要的化学性质。在高压极端条件下,氢"活泼好动",物理和化学性质显著变化,表现出金属性甚至超导等性质。本文介绍作者近年来见证、经历与推动的极端条件下氢元素化学发展的故事。     

高压化学

高压化学在现代科学中占有重要的地位,并在过去二十几年中取得了快速的发展。本文简要介绍了高压化学及高压化学研究领域在诸多方面的研究进展,其中包括高压无机化学和高压有机化学,以及高压在化学合成和化学过程研究中的应用,展示了高压化学的研究现状及其在许多方面的应用前景。     

Unicorns in the world of chemical bonding models

The appearance and the significance of heuristically developed bonding models are compared with the phenomenon of unicorns in mythical saga. It is argued that classical bonding models played an essential role for the development of the chemical science providing the language which is spoken in the territory of chemistry. The advent and the further development of quantum chemistry demands some restrictions and boundary conditions for classical chemical bonding models, which will continue to be integral parts of chemistry.     

Vapor pressure and intramolecular hydrogen bonding in fluorotelomer alcohols

Vapor pressure and aqueous solubility are important parameters used to estimate the potential for transport of chemical substances in the atmosphere. For fluorotelomer alcohols (FTOHs), currently under scrutiny by environmental scientists as potential precursors of persistent perfluorocarboxylates (PFCAs), vapor pressure is the more significant property since these compounds are only very sparingly soluble in water. We have measured the vapor pressures of a homologous series of fluorotelomer alcohols, F(CF2CF2)nCH2CH2OH (n = 2-5), in the temperature range 21-250 degrees C by three independent methods: (a) a method suitable for very low vapor pressures at ambient temperatures (gas-saturation method), (b) an improved boiling point method at controlled pressures (Scott method), and (c) a novel method, requiring milligram quantities of substance, based on gas-phase NMR, a technique largely unfamiliar to chemists and holding promise for studies of relevance to environmental chemistry. The concordant values obtained indicate that recently published vapor pressure data overestimate the vapor pressure at ambient temperature, and therefore the volatility, of this series of fluorinated compounds. It was suggested that substantial intramolecular -O-H...F- hydrogen bonding between the hydroxylic proton and the two fluorines next to the ethanol moiety was responsible for their putative high volatility. Therefore, we have used gas-phase NMR, gas-phase FTIR, 2D NMR heteronuclear Overhauser effect measurements, and high-level ab initio computations to investigate the intramolecular hydrogen bonding in fluorotelomer alcohols. Our studies unequivocally show that hydrogen bonding of this type is not significant and cannot contribute to and cause unusual volatility. The substantially lower vapor pressure at ambient temperatures than previously reported resulting from our work is important in developing a valid understanding of the environmental transport behavior of this class of compounds.     

Continuous Flow Organic Synthesis under High‐Temperature/Pressure Conditions

Microreactor technology and continuous flow processing in general are key features in making organic synthesis both more economical and environmentally friendly. When preformed under a high‐temperature/pressure process intensification regime many transformations originally not considered suitable for flow synthesis owing to long reaction times can be converted into high‐speed flow chemistry protocols that can operate at production‐scale quantities. This Focus Review summarizes the state of the art in high‐temperature/pressure microreactor technology and provides a survey of successful applications of this technique from the recent synthetic organic chemistry literature.     

Nehemiah Grew (1641–1712) and the Saline Chymistry of Plants

Abstract

In a series of lectures appended to his magisterial Anatomy of Plants (1682), Nehemiah Grew (1641–1712) explained the results of his own research into the saline chemistry of plants, following an established tradition in early modern chemistry. Members of the Royal Society such as Daniel Coxe were heavily involved in researching salt chemistry in the latter part of the seventeenth century, analysing the role of salts in spa waters, physiology, and as a fundamental element in iatrochemistry. Such researches of Royal Society members were often based upon the chemistry of Johann Van Helmont (1577–1634). As this paper will demonstrate, Grew's work drew from his microscopic research to elaborate and question some of Coxe's and hence Van Helmont's ideas about the principles of matter. Grew also used the results of his chemical research to draw conclusions about plant structure and colour, and applied his results to other areas in natural history such as meteorology, illustrating that chemistry was the basic analytical tool for seventeenth-century investigators of anatomy and natural history.     

Aromaticity and antiaromaticity in transition-metal systems

Aromaticity is an important concept in chemistry primarily for organic compounds, but it has been extended to compounds containing transition-metal atoms. Recent findings of aromaticity and antiaromaticity in all-metal clusters have stimulated further research in describing the chemical bonding, structures and stability in transition-metal clusters and compounds on the basis of aromaticity and antiaromaticity, which are reviewed here. The presence of d-orbitals endows much more diverse chemistry, structure and chemical bonding to transition-metal clusters and compounds. One interesting feature is the existence of a new type of aromaticity-delta-aromaticity, in addition to sigma- and pi-aromaticity which are the only possible types for main-group compounds. Another striking characteristic in the chemical bonding of transition-metal systems is the multi-fold nature of aromaticity, antiaromaticity or even conflicting aromaticity. Separate sets of counting rules have been proposed for cyclic transition-metal systems to account for the three types of sigma-, pi- and delta-aromaticity/antiaromaticity. The diverse transition-metal clusters and compounds reviewed here indicate that multiple aromaticity and antiaromaticity may be much more common in chemistry than one would anticipate. It is hoped that the current review will stimulate interest in further understanding the structure and bonding, on the basis of aromaticity and antiaromaticity, of other known or unknown transition-metal systems, such as the active sites of enzymes or other biomolecules which contain transition-metal atoms and clusters.     

主族元素AB4型含氧酸根的成键分析——推荐一个研究型计算化学实验

介绍了一个面向高年级本科生的研究型计算化学实验。主族元素AB4型含氧酸根是无机和结构化学理论课程中讨论化学键类型的例子,然而其结果却存在争议。本实验利用常用量子化学软件,通过计算化学方法分析化学成键,验证猜测,并得出结论。旨在通过本实验,锻炼学生对量子化学计算方法的运用,进而加深对化学基础知识的理解。     

Calcium Carbide: A Unique Reagent for Organic Synthesis and Nanotechnology

Acetylene, HC≡CH, is one of the primary building blocks in synthetic organic and industrial chemistry. Several highly valuable processes have been developed based on this simplest alkyne and the development of acetylene chemistry has had a paramount impact on chemical science over the last few decades. However, in spite of numerous useful possible reactions, the application of gaseous acetylene in everyday research practice is rather limited. Moreover, the practical implementation of high‐pressure acetylene chemistry can be very challenging, owing to the risk of explosion and the requirement for complex equipment; special safety precautions need to be taken to store and handle acetylene under high pressure, which limit its routine use in a standard laboratory setup. Amazingly, recent studies have revealed that calcium carbide, CaC₂, can be used as an easy‐to‐handle and efficient source of acetylene for in situ chemical transformations. Thus, calcium carbide is a stable and inexpensive acetylene precursor that is available on the ton scale and it can be handled with standard laboratory equipment. The application of calcium carbide in organic synthesis will bring a new dimension to the powerful acetylene chemistry.     

A fresh look at dense hydrogen under pressure. III. Two competing effects and the resulting intra-molecular H-H separation in solid hydrogen under pressure

A preliminary discussion of the general problem of localization of wave functions, and the way it is approached in theoretical condensed matter physics (Wannier functions) and theoretical chemistry (localized or fragment orbitals) is followed by an application of the ideas of Paper II in this series to the structures of hydrogen as they evolve under increasing pressure. The idea that emerges is that of simultaneously operative physical (reduction of available space by an increasingly stiff wall of neighboring molecules) and chemical (depopulation of the σ(g) bonding molecular orbital of H(2), and population of the antibonding σ(u)? MO) factors. The two effects work in the same direction of reducing the intermolecular separation as the pressure increases, but compete, working in opposite directions, in their effect on the intramolecular (nearest neighbor, intra-pair) distance. We examine the population of σ(g) and σ(u)? MOs in our numerical laboratory, as well as the total electron transfer (small), and polarization (moderate, where allowed by symmetry) of the component H(2) molecules. From a molecular model of two interacting H(2) molecules we find a linear relationship between the electron transfer from σ(g) to σ(u)? of a hydrogen molecular fragment and the intramolecular H-H separation, and that, in turn, allows us to estimate the expected bond lengths in H(2) under pressure if the first effect (that of simple confinement) was absent. In essence, the intramolecular H-H separations under pressure are much shorter than they would be, were there no physical/confinement effect. We then use this knowledge to understand how the separate E and PV terms contribute to hydrogen phase changes with increasing pressure.     

Predicting bondons by Goldstone mechanism with chemical topological indices

The Goldstone symmetry breaking algorithm is applied on ?² and ?⁴ chemical field contributions weighted, respectively, by the sphericity and extreme‐sphericity topological indices to provide for stable chemical bonding in the high temperature regime, the typical mass for the bondon, and the associated quantum boson. The method is applied to a representative series of polycyclic aromatic hydrocarbons providing an aromaticity hierarchy comparable with the scale‐based on the chemical hardness; present calculations on the bondonic mass place the physical existence of that bosonic‐bondonic quantum particle in the range of a few GeV and 10^?22 s, as typical for negatively charged massive bosons. © 2014 Wiley Periodicals, Inc.     

The Atom in the Chemistry Curriculum: Fundamental Concept, Teaching Model or Epistemological Obstacle?

Research into learners' ideas aboutscience suggests that school and collegestudents often hold alternative conceptionsabout `the atom'. This paper discusses whylearners acquire ideas about atoms which areincompatible with the modern scientificunderstanding. It is suggested that learners'alternative ideas derive – at least in part –from the way ideas about atoms are presented inthe school and college curriculum. Inparticular, it is argued that the atomicconcept met in science education is anincoherent hybrid of historical models, andthat this explains why learners commonlyattribute to atoms properties (such as beingthe constituent particles of all substances, orof being indivisible and conserved inreactions) that more correctly belong to otherentities (such as molecules or sub-atomicparticles). Bachelard suggested that archaicscientific ideas act as `epistemologicalobstacles', and here it is argued thatanachronistic notions of the atom survive inthe chemistry curriculum. These conceptualfossils encourage learners to develop an`atomic ontology' (granting atoms `ontologicalpriority' in the molecular model of matter); tomake the `assumption of initial atomicity' whenconsidering chemical reactions; and to developan explanatory framework to rationalisechemical reactions which is based on thedesirability of full electron shells. Theseideas then act as impediments to thedevelopment of a modern chemical perspective onthe structure of matter, and an appreciation ofthe nature of chemical changes at the molecularlevel.     

Photochemistry of Alkyltransition-Metal Complexes

Alkyltransition-metal complexes play an important role in catalytic processes (e.g. Ziegler-Natta low-pressure polymerization, hydroformylation, Fischer-Tropsch synthesis), in the biochemistry of humans and animals (e.g. coenzyme B₁₂), and in the classical theory of the chemical bond (e.g. multicenter bonding). The chemistry of alkyltransition-metal complexes is 30 years old, but only with the '70s came the understanding necessary for the systematic synthesis of thermally stable representatives of this class of compounds by blocking preferred decomposition pathways—e.g. β-hydrogen elimination—by the introduction of suitable ligands. In this article it is shown that thermally stable alkyltransition-metal complexes can be dealkylated under mild conditions (even at 12 K) with the help of UV light, thus producing highly reactive intermediates which can be trapped and used preparatively. Some alkyl complexes which do not react thermally with unsaturated compounds, e.g. olefins, under the influence of UV light display high activity as polymerization catalysts.     

Ab initio molecular dynamics simulations study on initial decompositions of β‐HMX at high temperature coupled with high pressures

We performed ab initio molecular dynamics simulations to investigate initial decomposition mechanisms and subsequent chemical processes of β‐HMX (cyclotetramethylene tetranitramine) (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) crystals at high temperature coupled with high pressures. It was found that the initial decomposition step is the simultaneous C–H and N–NO₂ bond cleavage at 3,500 K. When the pressure (1–10 GPa) is applied, the first reaction steps are primarily the C–N and C–H bond fission at 3,500 K. The C–H bond cleavage is a triggering decomposition step of the HMX crystals at 3,500 K coupled with 16 GPa. This indicates that the C–H bonds are much easier to be broken and the hydrogen radicals are much more active. The applied pressures (1–10 GPa) accelerate the decompositions of HMX at 3,500 K. The decomposition pathways and time evolution of the main chemical species demonstrate that the temperature is the foremost factor that affects the decomposition at high pressures (1–10 GPa). However, the decomposition of HMX is dependent on both the temperature (3,500 K) and the pressure (16 GPa). This work will enrich the knowledge of the decompositions of condensed energetic materials under extreme conditions.